Ace Frehley and Peter Criss do not have the stamina to pull off a reunion of KISS's original lineup, according to Gene Simmons.

The statement comes about a week after longtime Kiss manager, Doc McGhee, expressed doubts that Kiss's founding lineup would be able to agree on when or how to reunite.

Kiss's 'End of the Road' farewell tour is expected to conclude sometime early next year.

In a new interview with Chaozine, Simmons explained that he'd love to do a reunion but not optimistic.

"We've tried. I keep trying. Paul [Stanley[ and I met with Ace, trying to convince him to come back. He said, 'I want this. I want that.' Well, we can't do that," Simmons said.

He elaborated that while Frehley and Criss were invited on the tour, they were not invited to resume their former roles in the band full-time; they were invited to perform the encores with Simmons and Stanley.

It was a nonstarter.

"Ace said, 'No. The only way I'll come out is if I'm the Spaceman and you ask Tommy [Thayer] to leave.' I go, 'Well, that's not gonna happen.'"

Simmons adds that he still cares about Frehley and Criss as friends and as musicians who were crucial to building Kiss to what it is.

"Not everybody is designed to run a marathon," he added. "Some people are designed to be in a band for a year or two, or a few years, and then that's all they can do. And both of them have been in the band three different times. How many chances in life do you get? All I know is when I put my hand in fire the first time, I got burnt; I didn't get a second or third chance."

Despite his doubts, Simmons adds that "the door's always open," but a reunion will be on Kiss's terms, not on those of Frehley and Criss. Thayer and longtime Kiss drummer Eric Singer aren't going anywhere.

Frehley and Criss recently reunited in Nashville for a performance at Creatures Fest. Simmons, who says he watched a clip of the performance, described it as "very sad."

He explained that Criss's "health isn't what it should be. I don't want to get too specific because it's part of his private life. But no, physically, he wouldn't be able to do it. Neither would Ace."

See all of Kiss's tour dates here.